Fluorescent lamp-dimming circuit



Aug. 26, 1969 H. PRIVETT ErAL 3,463,964

FLUORESCENT LAMP-DIMMING cmcun' Filed Nov. 28, 1967 2 Sheets-Sheet 1 Fig.1.

BRIGHT HERBERT LAWRENCE PRIVETT HAROLD ROBERT RUFF INVENTORS BYWK ATTORNEY Aug. 26, 969 H. L. PRIVETT ETAL FLUORESCENT LAMP-DIMMING CIRCUIT Filed Nov. 28, 1967 2 Sheets-Sheet 2 n n u u n \a 0 n.

KRQQQ HERBERT LAWRENCE PRIVETT HAROLD ROBERT RUFF INVENTORS BY ATTORN EY 3,463,964 Patented Aug. 26, 1969 3,463,964 FLUORESCENT LAMP-DIMMING CIRCUIT Herbert L. Privett, Birstall, Leicester, and Harold R. Ruff,

London, England, assignors to British Lighting Industries Limited, London, England Filed Nov. 28, 1967, Ser. No. 686,050 Int. Cl. H05b 41/42 US. Cl. 315247 5 Claims ABSTRACT OF THE DISCLOSURE A light dimming circuit for gas lamps provides a high and low or dim state. In the high state the lamp is directly connected to the power supply through a ballast reactor. In the low state the lamp is connected to the high voltage terminal of an autotransformer through first and second resistors and a reactor. In the low state a transfer relay with its contacts makes the necessary connections. The primary winding of the autotransformer is permanently connected across the power supply and may also furnish the supply for the heaters of the lamp. Condensers for power factor, RF elimination, shimmering of lights and other purposes may be added if so desired.

The present invention relates to fluorescent lamp circuits which can be switched between bright and dim conditions of the lamp or lamps in the circuit.

In accordance with the invention there is provided a fluorescent lamp circuit including at least one lamp and a switch for switching the lamp between dim and bright conditions, the switch serving in one position to energise a relay which has a first set of contacts which in the dim condition of the switch cause the lamp to be fed through a resistor of high impedance to reduce the current through the lamp to a low value and a second set of contacts arranged when the switch is in its dim condition to apply an increased voltage to the lamp from a transformer to maintain the stability of the discharge when the lamp is being fed through the said resistor.

Preferably, the circuit includes a radio interference suppression capacitor connected across the lamp in conventional manner and in order to ensure that this is effective in both conditions of the circuit one pole of the capacitor is connected to the side of the said resistor remote from the lamp.

A capacitor may be connected across the said resistor to reduce shimmer in the lamp in the dim condition.

The invention will now be described in more detail with the aid of examples illustrated in the accompanying drawings in which:

FIG. 1 is a circuit diagram of a twin-lamp circuit in accordance with the invention, and

FIG. 2 is a circuit diagram of a single lamp circuit.

The circuit of FIG. 1 has two lamps and 11 which are supplied from live, neutral and earth terminals, L, N, and E of the electric mains supply. A ganged switch 12 connected to terminal L has a central off-position as shown, an upper bright position and a lower dim position. In both dim and bright positions the terminals L and N are connected to the primary winding 13 of a transformer which supplies heating current to the electrodes of the lamps 10 and 11 from secondary windings 14 and 15 and a tapping 16 on the winding 13. An auto-transformer 17 also has the lower part of its winding connected across the terminals L and N. One electrode of the lamp 10 is connected directly to the terminal N while the other electrode is connected through a resistor 18 shunted by relay contacts r1, a ballast choke 19, and relay contacts r2 to the terminal L through the switch 12. Similarly, one electrode of the lamp 11 is connected directly to terminal N and the other electrode through a resistor 20 shunted by relay contacts r3, a ballast choke 21 and capacitor 22, and relay contacts r2 to the terminal L through the switch 12.

In the bright position of the switch 12 the relay contacts r1, r2 and r3 are in the positions shown and the lamps are fed in conventional manner. When the switch 12 is placed in its dim position a relay coil R is energised, causing contacts 12 to change over and contacts r1 and r3 to open. The resistors 18 and 20 are thus placed in series with the lamps 10 and 11 respectively to reduce the current flowing through them to a value suitable for producing a dim light. The change-over of contacts 12 applies an increased voltage to the lamps from the auto-transformer 17 to maintain the stability of operation of the lamps at low current densities. A protective resistor 23 is connected in series between the contacts r2 and the autotransformer 17 to avoid excessive currents should the contacts r1 and r3 fail to open. To reduce shimmer of the lamps in the dim condition, capacitors 24 and 25 of small value are connected across the resistors 18 and 20 respectively.

Conventional radio interference suppression capacitors 26 and 27 are connected across the lamps 10 and 11, respectively. One pole of each of the capacitors 26 and 27 is connected directly to one electrode of the associated lamp and the other to the side of the resistor 18 or 20 remote from the lamp. Thus in the bright condition the capacitors 26 and 27 are connected directly between the electrodes of the lamps while in the dim condition each of them is connected across the associated lamp and the series resistor. Interference suppression is thus effective in both conditions of the circuit.

FIG. 2 shows a single lamp circuit corresponding to the circuit of FIG. 1 with the lamp 11 removed. The transformer 13 is omitted and the electrode heating current is taken from the transformer 17 The other circuit elements are largely the same as in FIG. 1, the same reference numerals having been used, and the manner of operation is fundamentally the same. The circuit of FIG. 2 contains a third set of contacts r3 of the relay R, which are connected in series with a power factor capacitor 28 across the live and neutral terminals and are closed while the circuit is in its bright condition. When the circuit is switched to the dim condition the power factor is improved by removal of the capacitor 28 from the circuit.

In a modification of the circuits shown, the choke 19 and the choke-capacitor combination 21 and 22 can be placed in series with the relay contacts r1 and r3 across the resistors 18 and 20 so that they are out of circuit in the dim. condition.

We claim:

1. A fluorescent lamp circuit comprising a lamp,

a switch for switching said lamp between dim and bright conditions,

a relay having first and second sets of contacts, a resistor of high impedance, and

a transformer connected to generate operating voltage across the lamp,

said relay being coupled to the switch for energisation in one position of the switch,

said first set of contacts connecting the resistor between the transformer and the lamp upon actuation of the switch to its dim condition, and

said second set of contacts connecting the transformer to apply an increased voltage to the resistor and lamp upon actuation of the switch to its dim condition to maintain stability of the lamp discharge at low currents.

2. A fluorescent lamp circuit as claimed in claim 1 in which said first set of contacts is in shunt with the said resistor.

3. A circuit as claimed in claim 1 comprising a capacitor connected across the said resistor to reduce shimmer in the lamp in the dim condition.

4. A circuit as claimed in claim 1 including a radio interference suppression capacitor connected across the lamp one pole thereof being connected to the side of the said resistor remote from the lamp.

5. A circuit as claimed in claim 1 comprising a power factor capacitor, said relay having a third set of contacts connected in series with said power factor capacitor across supply terminals of the circuit, said third set of contacts being open in the dim condition of the switch.

4 References Cited UNITED STATES PATENTS 2,665,394 1/1954 Arvidsson et al 31s-97 2,774,917 12/1956 Passmore 315-97 2,829,314 4/1958 Vradenburgh s1s 200 FOREIGN PATENTS 1,169,035 4/1964 Germany.

10 JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R. 

